CosmoELEMENTS

BLACK BEAUTY: A UNIQUE 4.4 GA, WATER-RICH METEORITE FROM MARS

Carl Agee* A polished FIGURE 3 Northwest Africa (NWA) 7034, and its pairings, surface of the interior of NWA is a new type of Martian meteorite discovered 7034 clearly exhibiting recently in Western Sahara. NWA 7034, also clasts of various known as “Black Beauty” because of its dark, lithologies set in a fi ne shiny appearance (FIG. 1), contains ten times grained matrix. PHOTO CREDIT: UNIVERSITY more water than other Martian meteorites. OF NEW MEXICO This, combined with its anomalous oxygen isotope values and ancient zircons, makes it an extraordinarily valuable specimen for under- standing surface processes, aqueous altera- tion, and atmosphere–lithosphere exchange reactions that existed on Mars as far back as 4.4 billion years ago. Black Beauty appears to be the fi rst Martian meteorite to match the sur- face geochemistry of Mars, as seen by landers and orbiters, and as such, it has particular rel- evance to the current Mars Science Laboratory mission at Gale Crater.

The main mass of NWA 7034. Both the FIGURE 2 fusion-crusted exterior and a sawn face showing the interior breccia are visible. PHOTO CREDIT: UNIVERSITY OF NEW MEXICO

At present, at least six different igneous rock types have been found in the 1–2 kg of the breccia now identifi ed as NWA 7034 (owing to new fi nds). These include basalt, trachyte, and andesite. These compositions are remark- Three hand samples of NWA 7034, the FIGURE 1 ably similar to the rocks analyzed by APXS Elemental SEM map of a thin section Martian meteorite known as Black Beauty FIGURE 4 of NWA 7034 showing clasts with clear due to its shiny black appearance. PHOTO CREDIT: on the Spirit Rover at Gusev Crater and more compositional differences. Red = Mg, green = K, blue = UNIVERSITY OF NEW MEXICO recently with ChemCam on the Mars Science Ca. IMAGE COURTESY OF ROMAIN TARTÈSE, OPEN UNIVERSITY Lab at Gale Crater. Thus Black Beauty is the Reported last year by a consortium of over a fi rst tangible sample of the surface of Mars dozen workers (Agee et al. 2013), NWA 7034 as determined by NASA missions. Secondary revealing the sequence of events that brought is the fi rst and only Martian meteorite breccia alteration products in clasts, spheres, and this breccia together, prior to its being blasted (FIG. 2). The original 320 g mass of NWA 7034 pebbles of Martian origin are abundant in off Mars around 11 million years ago. Indeed, was found by an anonymous nomad meteorite Black Beauty, and the water-bearing phases NWA 7034 is not simply a single meteorite hunter in 2011 in Western Sahara (considered include maghemite, ferrihydrite, phyllosili- sample; it is more like a Martian geologic fi eld by Morocco to be part of its country). The mete- cates, and apatite, which sum to approximately area all contained within one rock—and there orite changed hands between the nomads and 6000 ppm bulk water—10 to 30 times higher is still much to explore! meteorite dealers, who sent it to the University than in other Martian meteorites. of New Mexico for classifi cation. A Martian REFERENCES origin was suspected based on Fe/Mn ratios, Age determinations on Black Beauty reveal the breccia’s diversity and its complex origin, Agee CB and 15 coauthors (2013) Unique meteorite which are often used to distinguish planetary from early Amazonian Mars: water-rich basaltic basalts (Agee et al. 2013), and was confi rmed which likely refl ect surface processes operating breccia Northwest Africa 7034. Science 339: by the presence of noble gases matching those during a span of a few billion years of Martian 780-785 history. Rb/Sr dating of the bulk sample done of the Martian atmosphere (Cartwright et al. Bogard DD, Johnson P (1983) Martian gases in an 2013; Grady et al. 2014). This technique has at the University of New Mexico gave an age Antarctic meteorite? Science 221: 651-654 of ~2.1 Ga; however, bulk Sm/Nd dating done been the practice since Bogard and Johnson Cartwright JA, Ott U, Hermann S, Agee CB (2013) (1983) confi rmed EETA 79001 as being Martian at NASA Johnson Space Center gave an age NWA 7034 contains Martian atmospheric noble by comparing noble gases trapped in pockets of ~4.4 Ga. Humayun et al. (2013) reported gases. Lunar and Planetary Science Conference of impact melt glass with measurements of ancient zircon U–Pb ages of ~4.4 Ga, but they 44: Abstract 2314 the composition of the Martian atmosphere also found a younger population of zircon with Grady MM, Schwenzer SP, Verchovsky AB (2014) as measured directly by Viking landers. Black ages of ~1.7 Ga, and subsequent studies have The mantle, crust and atmosphere of Mars as illuminated by the light element geochemistry Beauty has a basaltic bulk composition but is found many apatite, zircon, and baddeleyite grains with ages of ~1.4 Ga. Luckily for the of NWA 7034. Lunar and Planetary Science made up of numerous clasts of various litholo- Conference 45: Abstract 2779 chronologists, Black Beauty has populations of gies set in a fi ne-grained matrix (FIGS. 3, 4). apatite and zircon throughout the matrix and Humayun M and 10 coauthors (2013) Origin and age of the earliest Martian crust from meteorite * University of New Mexico, Institute of Meteoritics, in most clasts, which is offering the opportu- NWA 7533. Nature 503: 513-516 Albuquerque, New Mexico, USA nity to date individual lithic domains, thus E-mail: [email protected]

ELEMENTS 168 JUNE 2014 Elucidating Questions of Geochemistry

ElucidatingTechniques Questions for Geochemistry of Geochemistry by Bruker

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